Acaricides are chemical toxicants designed to control members of the order Acarina, a group that includes ticks and mites. In this taxonomic category are arthropods that attack crops, that are ectoparasites on higher animals, and that transmit numerous disease organisms to man and other animals. Primarily because of the resistance phenomenon new acaricides presumably with modes of action different from those of existing compounds are frequently required. Currently there exists insufficient information on the mechanism of action and metabolism of acaricides in both target and nontarget organisms. Such information is essential to assess any hazards that could be associated with the use of these compounds for acarine control. Therefore, we propose to investigate the mechanism of action and metabolism of certain acaricides in mites, insects, and mammals. Studies will be conducted in vivo and in vitro, and radiolabeled acaricides will be used when necessary. Compounds examined will include chlordimeform and other formamidines, methomyl, oxamyl, and diflubenzuron. This comparative approach is desirable if new selective acaricides are to be designed based on observed differences in mechanism of action and/or metabolism between different organisms.